This section is intended to provide a background or context to the invention that is recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.
The following abbreviations that may be found in the specification and/or the drawing figures are defined as follows:
3GPP third generation partnership project
dB decibel
eNB evolved node B
GSM global system for mobile communications
HSPA high speed packet access
LTE long term evolution
MIMO multiple in, multiple out
MN matching network
Node B base station
OFDMA orthogonal frequency division multiple access
OMA open mobile alliance
OTA over the air
PA power amplifier
RFIC radio frequency integrated circuit
RX receiver or reception (also, Rx)
SAW surface acoustic filter
SC-FDMA single carrier, frequency division multiple access
TS technical standard
TX transmitter or transmission (also, Tx)
RAT radio access technology
RF radio frequency
WCDMA wideband code division multiple access
Many wireless devices contain a transceiver that is used for bidirectional radio frequency communication with other wireless devices. Such transceivers have one or more transmitter paths and one or more receiver paths. Because of presence of transmitter power in a duplex filter (a “duplexer” herein) of the transceiver, high transmitter (TX) to receiver (RX) isolation and attenuation requirements are needed. This leads to design challenges and high insertion loss in duplex filter RX path. Duplex filter RX path insertion loss is directly affecting (e.g., degrading) the receiver's sensitivity one to one (dB). More particularly, in a typical receiver, there is a filter before a low noise amplifier (LNA). The noise factor of the passive element (the filter) comes directly from loss of the component, and the first component in chain has a major effect on the noise factor and noise figure for the receiver. The bigger the RF loss before the LNA, the worse the noise figure and the receiver sensitivity.
Transmitter power is also heating the duplex filter, and this is causing frequency drift and additional insertion loss also at RX path of the duplex filter, because the entire component is heated. Duplex filter insertion loss is also higher with high temperature, even without the effect of shifted center frequency. Further, frequency drift and additional insertion loss at the RX side of the duplex filter are degrading sensitivity of the receiver.
Typically, the duplex filter is connected to an antenna switch and the antenna switch is connected to antenna. The antenna switch is used to select which transmitter or receiver path is coupled to the antenna. The antenna is common for both the transmitter and receiver in the transceiver, and it is not possible to fully optimize antenna performance to receiver frequencies without an effect on antenna performance at the transmitted frequency band.
In full duplex systems, the transmitter and receiver of the transceiver are active simultaneously and the transmitter signal is causing, together with spurious signals, intermodulation products directly to the operating band of the receiver. This causes additional impact on RX performance.
In OTA (over the air) performance evaluation of wireless devices, different use cases are tested, such as the following locations where the wireless device could be relative to human proximity:                free space (i.e., no human proximity);        in hand;        beside head; and        beside head with hand.        
The position of antenna is very important to achieve good OTA performance, but it is hard or impossible to find a position for an antenna that is good for all use cases.